1. Field of the Invention
The present invention relates to a display device, and, in particular, relates to a display device having a display surface with a functional film attached thereon.
2. Description of the Related Art
There is known a display device which has a liquid crystal panel with a functional film such as a touch panel that is adhered to a display surface. For example, JP2001-356323A (Document 1) describes a liquid crystal display device which has a liquid crystal panel to which a touch panel is adhered. In the liquid crystal display device, the liquid crystal panel and the touch panel adhered to each other by a pressure sensitive adhesive double coated tape or a seal material. The pressure sensitive adhesive double coated tape or the seal material is disposed so as to surround the display area of the liquid crystal panel.
JP2002-259052A (Document 2) describes a liquid crystal display device which has a liquid crystal display and a touch panel which adhered to each other via a seal material having a predetermined thickness. Further, in the liquid crystal display device described in document 2, a transparent gas is sealed between the liquid crystal display and the touch panel.
In the liquid crystal display device described in JP2002-259052, deflection of the touch panel is suppressed by the gas sealed between the liquid crystal display and the touch panel, and contact of the liquid crystal display and the touch panel is avoided.
JP2007-34736A (Document 3) describes a display device which has a display and a touch panel which are overlaid on each other via a plurality of glass beads. In the display device described in JP2007-34736A, distortion of the touch panel is reduced by the glass beads, and contact of the display and the touch panel is avoided.
JP09-274536A (Document 4) describes a manufacturing method of a display device which has the step of bonding a liquid crystal display element and a transparent touch switch to each other by a transparent adhesive. The manufacturing method has the step of applying a transparent adhesive to the center of the back surface of the transparent touch switch, the step of inverting the transparent touch switch, the step of slowly superimposing the back surface of the transparent touch switch coated with the transparent adhesive and the front surface of the liquid crystal display element, and the step of causing the transparent adhesive to flow between the back surface of the transparent touch switch and the surface of the liquid crystal display element.
An air layer is present between the liquid crystal panel and the touch panel of the liquid crystal display device described in document 1. Accordingly, the contrast is reduced by scattering and reflection of light by the air layer. Further, the touch panel is supported at only its peripheral edge portion, and therefore, if pressure is applied to the touch panel, the panel bends to be in contact with the liquid crystal panel, and unevenness in the display occurs.
In each of the display devices described in document 2 and document 3, the entire surface or the substantially entire surface of the touch panel is supported by the gas or glass beads, and therefore, deflection of the touch panel is suppressed. Therefore, one of the above described disadvantages that was pointed out concerning the liquid crystal display device described in document 1 is eliminated. However, the display devices are similar to the liquid crystal display device described in document 1 in the respect that the air layer is interposed between the liquid crystal display and the touch panel or between the display and the touch panel. Therefore, the disadvantage of reduction in contrast by scattering and reflection of light due to the air layer is not eliminated.
A transparent adhesive is charged in between the liquid crystal display element and the transparent touch switch of the display device manufactured by the manufacturing method described in document 4. In other words, an air layer is not present between the liquid crystal display element and the transparent touch switch. Accordingly, reduction in contrast due to scattering and reflection of light by the air layer does not occur. However, the manufacturing method described in document 4 has the step of superimposing the back surface of the transparent touch switch coated with the transparent adhesive on the front surface of the liquid crystal display element, and the step of causing the transparent adhesive to flow between the back surface of the transparent touch switch and the front surface of the liquid crystal display element. Accordingly, the transparent adhesive spreads from the centers of the transparent touch switch and the liquid crystal element toward the end portions. In this case, the thickness of the transparent adhesive in the center becomes larger than that in the end portion, and an adverse effect is likely to occur in the display quality. Further, the transparent adhesive which spreads toward the end portions of the transparent touch switch and the liquid crystal display element are likely to flow outside and adhere to the front surface of the transparent touch switch or the back surface of the liquid crystal display element.